U.S. patent number 8,986,506 [Application Number 13/977,258] was granted by the patent office on 2015-03-24 for shoe press belt.
This patent grant is currently assigned to Valmet Technologies, Inc.. The grantee listed for this patent is Vesa-Matti Riihioja. Invention is credited to Vesa-Matti Riihioja.
United States Patent |
8,986,506 |
Riihioja |
March 24, 2015 |
Shoe press belt
Abstract
A shoe press belt, and a method for manufacturing and using it.
The press belt comprises a base formed of heat-resistant elastomer,
inside which base there is a support structure comprising a
plurality of support yarns. At least some of the support yarns are
heat-resistant polymer yarns, the polymer structure of the material
of which comprises a naphthalene group.
Inventors: |
Riihioja; Vesa-Matti (Tampere,
FI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Riihioja; Vesa-Matti |
Tampere |
N/A |
FI |
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Assignee: |
Valmet Technologies, Inc.
(Tampere, FI)
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Family
ID: |
43528582 |
Appl.
No.: |
13/977,258 |
Filed: |
January 30, 2012 |
PCT
Filed: |
January 30, 2012 |
PCT No.: |
PCT/FI2012/050076 |
371(c)(1),(2),(4) Date: |
June 28, 2013 |
PCT
Pub. No.: |
WO2012/104480 |
PCT
Pub. Date: |
August 09, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20130269895 A1 |
Oct 17, 2013 |
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Foreign Application Priority Data
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Jan 31, 2011 [FI] |
|
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20115099 |
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Current U.S.
Class: |
162/358.4;
442/333; 442/414; 162/358.3; 162/901 |
Current CPC
Class: |
D21F
3/00 (20130101); D21F 3/0227 (20130101); D21F
3/0236 (20130101); B29C 41/20 (20130101); D21G
1/006 (20130101); Y10S 162/901 (20130101); Y10T
442/696 (20150401); Y10T 442/607 (20150401) |
Current International
Class: |
D21F
3/02 (20060101); D21G 1/00 (20060101) |
Field of
Search: |
;162/358.1-358.4,900-901,348 ;442/328,333,358,374,414 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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43 28 029 |
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Feb 1995 |
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DE |
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WO 2010/066950 |
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Jun 2010 |
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WO |
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WO 2012104480 |
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Aug 2012 |
|
WO |
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Other References
May 24, 2012 International Search Report issued in International
Patent Application No. PCT/FI2012/050076. cited by applicant .
Sep. 9, 2011 Finnish Search Report issued in Finland Patent
Application No. 20115099 (with translation). cited by applicant
.
May 24, 2012 Written Opinion issued in International Patent
Application No. PCT/FI2012/050076. cited by applicant.
|
Primary Examiner: Fortuna; Jose
Attorney, Agent or Firm: Oliff PLC
Claims
The invention claimed is:
1. A shoe press belt which is an independent piece with a shape of
an endless loop, runnable in a shoe press through a long nip
between at least one roll and a press shoe, the shoe press belt
comprising: a base which is of an elastomeric heat-resistant
material; a plurality of polymeric support yarns arranged in at
least one yarn layer inside the base; and a first surface on the
side of the press shoe, and a second surface on the side of a fibre
web, wherein at least some of the support yarns are heat-resistant
polymer yarns, the polymer structure of the material of which
comprises a naphthalene group, wherein the structure of said
heat-resistant polymer yarn comprises completely aromatic liquid
crystalline polymer, the completely aromatic liquid crystalline
polymer being poly(4-hydroxybenzoic acid-co-6-hydroxy-2-naphthoic
acid) and the glass transition temperature Tg of said polymer
material is at least 110.degree. C., wherein the shoe press belt is
impermeable, and wherein the force required for a 2-% stretch of
said heat-resistant polymer yarn is at least 10 cN/tex, 20.degree.
C.
2. The shoe press belt as claimed in claim 1, wherein the force
required for a 2-% stretch of the yarn being at least 100
cN/tex.
3. The shoe press belt as claimed in claim 1, wherein at least the
support yarns of the yarn layer closest to the first surface on the
side of the press shoe are heat-resistant yarns.
4. The shoe press belt as claimed in claim 1, wherein the press
belt comprises at least one machine-direction yarn layer and at
least one cross-machine-direction yarn layer; and at least the
support yarns of the machine-direction yarn layer closest to the
first surface on the side of the press shoe are disclosed
heat-resistant yarns.
5. The shoe press belt as claimed in claim 1, wherein the base
comprises heat-resistant polyurethane polymer.
6. The shoe press belt as claimed in claim 1, wherein the base
comprises heat-resistant polyurethane polymer, and the polyurethane
polymer is made of urethane prepolymer containing isocyanate groups
and of a chain extender mixture, whereby 1,4-phenylene diisocyanate
is used for making the urethane prepolymer, and the chain extender
mixture comprises over 25% by weight
methyl-bis(3-chloro-2,6-diethylaniline).
Description
BACKGROUND OF THE INVENTION
The invention relates to a shoe press belt which may be used in
shoe presses of press sections of board, paper and pulp machines
and in a shoe press of the calender of a paper machine. A shoe
press belt is an independent belt-like piece with a shape of an
endless loop. The shoe press belt has a base of an elastomeric
material, and a support structure comprising support yarns inside
the base.
Further, the invention relates to a method for manufacturing a shoe
press belt and to the use of such a belt in a shoe press.
In chemical pulp, board and paper machines, shoe presses may be
used for removing water from a fibre web. In such shoe presses, one
surface of the wet fibre web travelling at a high speed is pressed
with a rotating press roll at the same time as a second surface of
the fibre web is pressed with an immobile press shoe surrounded by
an endless press belt. The inner surface of the press belt slides
against a sliding surface of the press shoe. As a result of this
sliding, the temperature of the press belt rises. Therefore, shoe
presses are typically provided with a lubrication assembly with
which lubricating oil can be supplied between the belt and the
press shoe to reduce generation of friction and heat. The heat
resistance of press belts has, however, turned out
insufficient.
BRIEF DESCRIPTION OF THE INVENTION
An object of this invention is to provide a shoe press belt of a
novel type, a method for manufacturing it, and use of a shoe press
belt of a novel type.
The press belt according to the invention is characterized in that
at least some of the support yarns are heat-resistant polymer
yarns, the polymer structure of the material of which comprises a
naphthalene group, and that the force required for a 2-% stretch of
said heat-resistant polymer yarn is at least 10 cN/tex, 20.degree.
C.
The method according to the invention is characterized by using, in
the support structure, heat-resistant support yarns which are
polymer yarns, the polymer structure of the material of which
comprises a naphthalene group, and with which support yarns the
force required for a 2-% stretch is at least 10 cN/tex, 20.degree.
C.
The use according to the invention is characterized in that a press
belt according to independent claim 1 is arranged in a shoe press
and run through a long nip between the press shoe and the press
roll, allowing an operating temperature of more than 80.degree.
C.
An idea is that the press belt has a base manufactured of a
heat-resistant material, inside which a support structure is
arranged that comprises a plurality of heat-resistant support
yarns. The heat-resistant support yarn is of such a polymer whose
polymeric structure comprises a naphthalene group. The yarn
comprising such a material has a relatively great force resisting
the stretch, in other words its yield strength is high. Further,
this strength property is preserved at a raised temperature. Thus,
the heat-resistant support yarn is selected to be a polymer yarn
with which the force required for a 2-% stretch is 10 cN/tex,
20.degree. C., or greater than that.
An advantage is that the press belt of the novel type is suitable
for use at a temperature higher than before. The shoe press can
thus be run at a higher operating temperature. This allows the
running speed and compression pressure of the shoe press to be
increased to improve the efficiency of the shoe press. Further, as
the press belt withstands higher temperatures without getting
damaged, it becomes possible to reduce the cooling of the lubricant
supplied between the press shoe and the press belt.
The idea of an embodiment is that the glass transition temperature
Tg of said heat-resistant polymer yarn is at least 80.degree.
C.
The idea of an embodiment is that the glass transition temperature
Tg of said heat-resistant polymer yarn is at least 100.degree.
C.
The idea of an embodiment is that said heat-resistant polymer yarn
comprises polyethylene naphthalate (PEN). The molecule structure of
this material is shown below. As can be observed, the material
comprises a naphthalene group that is shown as a pair of benzene
rings in the structural figure.
##STR00001##
The idea of an embodiment is that said heat-resistant polymer yarn
is of polyethylene naphthalate (PEN). The glass transition
temperature Tg of polyethylene naphthalate is 120.degree. C.,
whereby the strength properties of the PEN yarn are preserved well
also at a raised temperature. Proportioned to the linear density,
the breaking strength of polyethylene naphthalate is about 60
cN/tex. The stretch value with a stretch of 2% and at a temperature
of 20.degree. C. is more than 16 cN/tex, which is, for example,
about twofold compared with the corresponding value of polyester
comprising polyethylene terephthalate (PET), which is commonly used
as a support yarn. The stretch force of polyethylene naphthalate is
also at a temperature of 100.degree. C. about twofold compared with
polyethylene terephthalate. Thus, the material is strong and tough
and preserves its properties well also at raised temperatures.
Further, a support yarn made of polyethylene naphthalate has turned
out to have good strength properties against cross-direction
pressing of the yarn, in other words it has cross-directions
elasticity, owing to which the support yarn is highly resistant to
cross-direction impacts and stresses without breaking.
The idea of an embodiment is that said heat-resistant support yarn
is a copolymer comprising polyethylene naphthalate and one or more
second polymers suitable for the purpose.
The idea of an embodiment is that the structure of said
heat-resistant polymer yarn is of completely aromatic liquid
crystalline polymer, poly(4-hydroxybenzoic
acid-co-6-hydroxy-2-naphthoic acid). The molecule structure of such
a material is shown below. As can be observed, the material
comprises a naphthalene group that is shown as a pair of benzene
rings in the structural figure.
##STR00002##
The idea of an embodiment is that said heat-resistant polymer yarn
is heat-resistant yarn under the trade name Vectran. The glass
transition temperature Tg of such a support yarn is 110.degree. C.
or even higher, in other words the yarn preserves its properties
also at fairly high temperatures. Further, such a yarn has an
extremely great strength because the force required for a 2-%
stretch of the yarn is up to 100 cN/tex, 20.degree. C. or greater
than that. In an experiment, a stretch value of 2%, 115 cN/tex,
20.degree. C. was measured for the yarn.
The idea of an embodiment is that at least the yarns of a support
yarn layer closest to the surface on the side of the press shoe are
disclosed heat-resistant support yarns. This is because the support
yarns closest to the press shoe are subjected to the greatest
thermal stress from the sliding surface. Between the yarn layers
farther from the sliding surface and a first surface to be arranged
against the sliding surface, there is a greater thickness of base
material, which insulates heat transfer in the structure,
protecting thus the support yarns positioned farther away. The
support yarns closest to the sliding surface of the press shoe may
be in the machine direction or in the cross-direction relative to
the press belt.
The idea of an embodiment is that the press belt may comprise at
least one machine-direction support yarn layer and at least one
cross-machine-direction support yarn layer. At least the support
yarns of the machine-direction yarn layer closest to the surface on
the side of the press shoe are disclosed heat-resistant support
yarns. The machine-direction support yarns are subjected to greater
stresses, for instance tensile stresses, during operation, due to
which their durability may be critical with regard to the condition
and service life of the press belt.
The idea of an embodiment is that the support structure of the
press belt comprises at least one support fabric. The support
fabric comprises disclosed heat-resistant yarns. If required, all
yarns of the support fabric may be disclosed heat-resistant
yarns.
The idea of an embodiment is that all support yarns of the support
structure of the press belt are disclosed heat-resistant yarns.
The idea of an embodiment is that all support yarns of the press
belt are of polyethylene naphthalate (PEN) or yarns marketed under
the trade name Vectran.
The idea of an embodiment is that the base of the press belt
comprises polyurethane polymer made of a urethane prepolymer
containing isocyanate groups and of a chain extender. In
manufacturing the urethane prepolymer, 1,4-phenylene diisocyanate
(PPDI) has been used, and the chain extender comprises
methyl-bis(3-chloro-2,6-diethylaniline) (MCDEA). MCDEA is, in the
field, also referred to as
4,4'-methylene-bis(3-chloro-2,6-diethylaniline). Urethane
prepolymer refers to a product obtained from a reaction between
said 1,4-phenylene diisocyanate monomer (PPDI) and a polyol. To
make an urethane prepolymer, PPDI is reacted with a polyol. The
polyol used may be any polyol commonly used in making
polyurethanes. Thus, the polyol may be, for example, polyether
polyol, polyester polyol, polyether carbonate polyol, polycarbonate
polyol or polycaprolactam polyol. When, in addition to symmetrical
PPDI, a chain extender containing symmetrical MCDEA is used for
making polyurethane, the heat-resistance properties of a shoe press
belt made of such a polyurethane are excellent. For example, the
breaking strength of the belt is preserved at a raised temperature,
and other properties of the polyurethane belt, such as wear
resistance and recovery from compression, may also be improved. For
the sake of clarity, this polyurethane polymer may, in this
application, be also called PPDI urethane.
The idea of an embodiment is that the press belt is manufactured in
a casting drum by using centrifugal casting. Hence, support yarns
are first placed on the inner surface of the casting drum and then,
while the drum is rotating, a polyurethane material or a
corresponding elastomer is uniformly applied around and onto the
support yarns. There may be several yarn layers, in which case
after arranging each yarn layer, a new centrifugal casting may be
carried out in the casting drum. Thus, the yarn layers are not in
contact with each other but there is cast elastomer between
them.
The idea of an embodiment is that the press belt is manufactured in
a casting drum by using centrifugal casting. First, a first casting
layer is cast from a heat-resistant elastomer. The first casting
layer may be cast without support yarns or with support yarns.
After that, cross-machine-direction yarns are arranged and a second
casting layer is cast. The machine-direction support yarns may be
arranged at the same time as the second casting layer is cast.
Finally, yet one or more coating layers may be cast.
The idea of an embodiment is that the base of the press belt is
manufactured by casting heat-resistant elastomer onto a casting
cylinder. As the support yarns in the circumferential direction,
above-mentioned polymer yarns may be used which have a structure of
completely aromatic liquid crystalline polymer,
poly(4-hydroxybenzoic acid-co-6-hydroxy-2-naphthoic acid). Further,
the heat-resistant support yarns in the circumferential direction
may be yarns which are marketed under the trade name Vectran and
have a glass transition temperature Tg of at least 110.degree. C.,
the force required for a 2-% stretch of the yarn being at least 100
cN/tex, 20.degree. C.
The idea of an embodiment is that the support structure inside the
base is a non-woven structure in which the support yarns do not
cross and bind to each other.
BRIEF DESCRIPTION OF THE FIGURES
Some embodiments will be explained in more detail in the attached
drawings, in which
FIG. 1 shows schematically the principle of a shoe press;
FIG. 2 shows schematically a press belt which is an independent
component that is manufactured separately, has a shape of a closed
loop and may be mounted on a shoe press;
FIGS. 3a and 3b show schematically a cross-section of a part of a
press belt and its support structure;
FIG. 4 illustrates, as a simplified diagram, features disclosed in
this application; and
FIGS. 5a and 5b further show schematically a cross-section of some
alternative ways to arrange the support yarn layers and elastomer
layers in the press belt.
In the figures, some embodiments are shown in a simplified manner
for the sake of clarity. Like reference numerals identify like
elements in the figures.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
FIG. 1 shows a simplified shoe press 1 which may comprise a press
roll 2 and a press shoe 3, between which there is a press zone 4
through which a press belt 5, at least one paper machine fabric 6,
7 and a fibre web 8 to be dried may be arranged to be run in the
machine direction MD. The press shoe 3 and the press roll 2 may be
pressed against each other with a force F, whereby the press belt
5, the paper machine fabric 6, 7 and the fibre web 8 run between
them are compressed. The press shoe 3 has a curved sliding surface
L facing the press roll 2, whereby there is an extended contact
area, i.e. what is called a long nip, between the press shoe 3 and
the press roll 2. The press belt 5 may be arranged to pass around
the press shoe 3, supported by an appropriate support member 9. An
inner surface 10 of the press belt 5 slides against the sliding
surface L of the press shoe 3, and an outer surface 11 of the belt
faces the fibre web 8. The fibre web 8 may be brought to the press
zone 4 in such a way that it is supported by one or more paper
machine fabrics, such as a press felt 7 or a wire 6. The paper
machine fabric 6, 7 may be run in such a way that it is guided by
guide rolls 12 or the like. In the embodiment according to FIG. 1,
the upper paper machine fabric may be a press belt 7 and the lower
fabric may be a wire 6. When the fibre web 8 passes through the
relatively long press zone 4 formed by the press roll 2 and the
press shoe 3, water is pressed out of it which may be received by
the press felt, from which the water may be removed by a water
collecting device 13, for instance.
Between the sliding surface L of the press shoe 3 and the inner
surface 10 of the press belt 5, there is friction, and it is
possible to try to reduce it by supplying lubricant between the
press shoe 3 and the press belt 5 by means of a lubrication system
V. Oil, for example, may be used as the lubricant. The friction
between the sliding surface L and the press belt 5 generates heat
which heats the lubricating oil of the press shoe 3 and also raises
the temperature of the press belt 5. The lubrication system V may
comprise a cooling system J to cool the lubricant. The cooled
lubricant allows generation of heat in the sliding surface L and
heat transfer to the press belt 5 to be reduced. The intention of
cooling the lubricant is to ensure that the temperature of the
press belt 5 will not rise over the allowed operating temperature,
which is typically approximately 60 to 70.degree. C. However, the
cooling consumes a large amount of energy. Further, the cooling
equipment J complicates the structure of the shoe press 1 and
requires maintenance. In objects of use in a warm climate, in
particular, arranging the cooling of the lubricant has turned out
rather problematic. The press belt 5 that is presented in this
application and comprises heat-resistant elastomer and
heat-resistant support yarns is designed to withstand a temperature
of more than 80.degree. C. and even a temperature of more than
100.degree. C. without the strength properties of the press belt 5
essentially changing. The use of such a heat-resistant press belt 5
in the shoe press 1 allows the cooling of the lubricant to be
reduced or even the cooling to be eliminated completely. As a
result, the energy efficiency of the shoe press 1 may be improved
and, in addition, it may even be possible to simplify the
construction of the shoe press 1.
It is to be noted that the press belt disclosed in this application
is also applicable to shoe presses different from the one shown in
FIG. 1. What is common to different embodiments is that the press
belt is always a component which is manufactured separately and has
a shape of an endless loop, and which is arranged or may be
arranged in a shoe press in such a way that it passes through a
long nip between at least one roll and the press shoe, contributing
thus to the treatment of a fibre web.
FIG. 2 shows a press belt 5 of a shape of an endless loop, having
an inner surface 10 and an outer surface 11. The press belt 5 may
be arranged in the shoe press 1 such that its outer surface 11,
i.e. the second surface, faces the fibre web 8 while its inner
surface 10, i.e. the first surface, slides against the sliding
surface of the press shoe 3. FIG. 2 also illustrates, by broken
lines, a support structure 15 which is positioned inside the base
14 and which may comprise a yarn layer 17a comprising several
machine-direction MD support yarns 16, and a yarn layer 17b
comprising several cross-machine-direction CMD support yarns 18.
There may be one, two, three or more yarn layers 17. The number of
yarn layers 17 and the mutual order of the machine-direction yarn
layers 17a and the cross-machine-direction yarn layers 17b can be
selected according to the need.
The structure of a press belt 5 is shown in FIG. 3a in sectional
view in the machine direction MD and in FIG. 3b in sectional view
in the cross-machine direction CMD. The presented structure
comprises three support yarn layers 17a, 17b, 17c, arranged in such
a way that the machine-direction yarn layers 17a and 17c are in the
outermost position, and between them there is the middle
cross-machine-direction yarn layer 17b. Such a support structure 15
has turned out good. Alternatively, the support structure 15 may be
of a different kind, and it may comprise one, two, three or more
yarn layers on top of each other, and the mutual order and
directions of the yarn layers may be designed case-specifically.
Each yarn layer 17 comprises several adjacent yarns, which may be
separate support yarns or, alternatively, one or more support yarns
may be bound spirally side by side in a yarn layer. The yarn layers
17 on top of each other may be separate from one another, in which
case there is elastomer belonging to the base 14 between the yarn
layers. The material of the base 14 may be PPDI urethane disclosed
in this application. In some cases, the support structure 15 may
also be a fabric, in which case it may be considered to form one
yarn layer. The support yarns of the support structure 15 may be
monofilaments or multifilaments.
The yarn layer 17a closest to the press shoe 3 is, due to the
friction generated on the sliding surface L, subjected to the
greatest thermal stress. Thus, heat-resistant support yarns may be
arranged at least in this layer. Since the machine-direction yarns
are subjected to the greatest stresses during operation,
heat-resistant yarns may, if required, be used as all
machine-direction support yarns. If there is a
cross-machine-direction yarn layer closest to the press shoe 3 in
the support structure 15, heat-resistant support yarns may be used
in the cross-machine direction. Further, all support yarns of the
support structure 15 may be heat-resistant yarns. Heat-resistant
support yarns refer to support yarns disclosed in this application,
the polymer structure of the material of these yarns comprising a
naphthalene group. The support yarn may thus comprise polyethylene
naphthalate (PEN), in other words it is either completely of
polyethylene naphthalate or is one of its copolymers. Further, the
heat-resistant support yarn may comprise liquid crystalline polymer
(LCP) which is marketed under the trade name Vectran. If the
support structure has also yarns other than disclosed
heat-resistant support yarns, the material of these yarns may be,
for example, polyethylene terephthalate (PET), polyamide,
polypropylene or polyethylene.
Press belts are subjected to great stresses due to both compression
and, in particular, bending in different directions in the press
zone. These stresses may cause cracks to the base material of the
belt which gradually make the belt unusable. Further, in a paper
machine, fibre bundles may be generated which, while passing
through the press, generate sudden deformation forces which may
break the press belt. Further, fibre bundles may generate permanent
elongations and bulges in the belt. Therefore, the support yarns
must have a sufficiently high yield limit, which is typically
determined, in the case of polymer yarns, by means of stretch
force. If a fibre bundle, for example, generates in the press belt
and its support yarns deformation that locally exceeds the yield
limit, permanent elongation remains in the support yarns, and a
bulge remains in the press belt. A stretch value of 16 cN/tex with
a 2-% stretch and at a temperature of 20.degree. C. has been
designed for the PEN yarn. A force greater than this may cause
permanent deformation in the yarn. In practice, it has been noted
that the stretch value should be at least 10 cN/tex with a 2-%
stretch, 20.degree. C. Further, the glass transition temperature Tg
of the PEN yarn is 120.degree. C. The glass transition temperature
of the heat-resistant yarn should be at least 100.degree. C.,
whereby the material preserves its properties well at a raised
temperature of the shoe press, i.e. at over 80.degree. C., even at
over 100.degree. C. The glass transition temperature Tg refers to
reversible change of the non-crystalline (amorphous) part of a
polymer from rubber-like or tough state into hard and brittle.
The shoe press belt disclosed in this application may be
manufactured by using various manufacturing techniques. The press
belt may be manufactured by means of what is called centrifugal
casting in a drum. In such a case, the cross-machine-direction and
machine-direction support yarns may be first placed on the inner
surface of the casting drum and then, while the drum is rotating,
the PPDI urethane or the like heat-resistant elastomer is uniformly
applied around and onto the yarns. Further, it is feasible to cast
the construction in such a way that a first heat-resistant urethane
layer is cast with support yarns or without support yarns, after
which the cross-machine-direction support yarns are arranged,
followed by casting of a second urethane layer and simultaneous
positioning of the machine-direction support yarns in the
construction, and subsequently yet one or more urethane layers may
be cast in the casting drum, which layers cover the structural
layer comprising the machine-direction yarns. To illustrate casting
layers of the base 14, layers are denoted with reference numerals
14a to 14c in FIGS. 3a, 5a and 5b.
Alternatively, the press belt may be manufactured by casting it
onto a casting cylinder. In this arrangement, the machine-direction
support yarns are first arranged upon the casting cylinder and
subsequently elastomer material is cast onto the cylinder while the
cylinder is rotating, at the same time as the support yarn in the
circumferential direction is coiled up onto the machine-direction
yarns. Yet a third possibility is to manufacture the press belt in
such a way that the basic fabric is impregnated with an elastomer
in a cylindrical mould, whereby the basic fabric is placed between
the outer casing and the mandrel of the mould. Negative pressure is
sucked into the mould, after which the base material is injected
into the mould. The elastomeric material is thus uniformly absorbed
into the basic fabric. The shoe press belt may also be manufactured
by impregnating and/or coating a support structure that is woven,
braided or laminated endless on both sides with a heat-resistant
elastomer.
The embodiments shown in FIGS. 5a and 5b may, for the most part,
correspond to the above embodiments. The difference as compared
with the embodiment of FIG. 3a is the number and mutual order of
the yarn layers 17a to 17c belonging to the support structure 15.
Cross-machine-direction CMD and machine-direction MD elongation may
be generated in the press belt 5, due to fibre bundles, for
example. Cross-machine-direction deformation may, to some extent,
be compensated for during operation by tightening the shoe press
belt in the cross-machine-direction but, by contrast, compensating
for a machine-direction deformation is difficult. Therefore, there
is reason to use heat-resistant support yarns disclosed in this
application as the machine-direction yarns. The
cross-machine-direction yarns may also be such heat-resistant yarns
or, in some cases, they may be of another material. In FIG. 5b, for
instance, closest to the sliding surface L there is the
cross-machine-direction yarn layer 17b that may in some cases be
formed of ordinary support yarns. If cross-direction elongation is
generated in the belt 5, the belt may be tightened in the
cross-machine direction by moving the fastening members in the shoe
press unit away from one another. The embodiments of FIGS. 5a and
5b may be manufactured by casting in a drum or also by using other
manufacturing techniques mentioned above.
In some cases, features disclosed in this application may be used
as such, irrespective of other features. On the other hand, when
necessary, features disclosed in this application may be combined
to provide different combinations.
The drawings and the related description are only intended to
illustrate the idea of the invention. The details of the invention
may vary within the scope of the claims.
* * * * *